The present invention relates to a master cylinder, and more particularly, to a master cylinder capable of obtaining an increased braking force by intensifying a master cylinder pressure when required.
A braking system for automobiles which is found in the prior art is provided with a booster which utilizes a fluid pressure such as a negative pressure or a liquid pressure to boost an input to a given magnitude so that the increased output from the booster acts upon a master cylinder to cause it to produce a master cylinder pressure, thereby allowing a braking force of an increased magnitude to be obtained in response to a force of a small magnitude with which a brake pedal is depressed.
A conventional brake system incorporating a negative pressure booster utilizes a negative pressure which obtains in an engine. However, with a recent trend toward a lower fuel cost of the engine, the magnitude of the negative pressure which is developed in the engine is reduced with a consequent reduction in the output from the negative pressure booster. Such a reduction in the output may be compensated for by providing a negative pressure booster of an increased size, but it is difficult to provide a space in an engine room which accommodates a negative pressure booster of an increased size.
On the other hand, a brake incorporating a liquid pressure booster requires components such as a pump or an accumulator, disadvantageously leading to a cost increase of the overall system.
It is desirable for a brake system of the kind described to develop a braking force of an increased magnitude more rapidly during a quick braking operation than in a normal, more gentle braking operation.
It is recognized that a quick braking operation has a need for the development of an increased braking force. Nevertheless an unexperienced driver such as a beginner of driving an automobile may not be able to depress a brake pedal deep enough to develop an increased braking force. In such an instance, it is desirable that an assistance be afforded, even to an unexperienced driver, to enable him to develop an increased braking force in a reliable manner.
The present invention has been made in view of the foregoing and has for its object the provision of a master cylinder having a reduced number of parts with a simple and inexpensive construction to allow a reduction in its size while allowing an increased braking force to be obtained by intensifying a master cylinder pressure when necessary.
Specifically, according to a first aspect of the present invention defined in Claim 1, there is provided a master cylinder comprising a master cylinder piston slidably fitted into a housing to generate a master cylinder pressure, a thrust piston slidably fitted into the housing and disposed in abutment against the rear side of the master cylinder piston, an intensifying chamber defined within the housing rearwardly of the thrust piston, an input shaft adapted to move back and forth in interlocked relationship with a brake operating member, a source of liquid pressure adapted to be brought into communication with the intensifying chamber as required, a discharge passage providing a communication between the intensifying chamber and a reservoir for discharging an operating liquid in the intensifying chamber into the reservoir, and a control valve responsive to the input shaft to cause a liquid pressure to be generated in the intensifying chamber in accordance with an input applied to the input shaft by regulating a quantity of the operating liquid which is discharged from the intensifying chamber into the reservoir through the discharge passage, the discharge passage having an opening toward the intensifying chamber which is formed in the thrust piston, the opening cooperating with the front end of the input shaft to define the control valve.
According to a second aspect of the present invention defined in Claim 2, there is provided a master cylinder comprising a master cylinder piston slidably fitted into a housing to generate a master cylinder pressure, a thrust piston slidably fitted into the housing and disposed in abutment against the rear side of the master cylinder piston, an intensifying chamber defined within the housing rearwardly of the thrust piston, an input shaft adapted to move back and forth in interlocked relationship with a brake operating member, a source of liquid pressure adapted to be brought into communication with the intensifying chamber as required, a discharge passage providing a communication between the intensifying chamber and a reservoir for discharging an operating liquid in the intensifying chamber into the reservoir, and a control valve responsive to the input shaft to cause a liquid pressure to be generated in the intensifying chamber in accordance with an input applied to the input shaft by regulating a quantity of the operating liquid which is discharged from the intensifying chamber into the reservoir through the discharge passage, the thrust piston and the input shaft being in a slidable engagement while maintaining a liquid tightness therebetween, a valve chamber being defined between the thrust piston and the input shaft, the discharge passage extending through the valve chamber, the control valve being disposed in the valve chamber to open or close the discharge passage.
According to a third aspect of the invention defined in Claim 3, there is provided a master cylinder comprising a master cylinder piston slidably fitted into a housing to generate a master cylinder pressure, an intensifying chamber defined within the chamber rearwardly of the master cylinder piston, an input shaft adapted to move back and forth in interlocked relationship with a brake operating member, a source of liquid pressure adapted to be brought into communication with the intensifying chamber as required, a discharge passage providing a communication between the intensifying chamber and a reservoir for discharging an operating liquid in the intensifying chamber into the reservoir, and a control valve responsive to the input shaft to cause a liquid pressure to be generated in the intensifying chamber in accordance with an input applied to the input shaft by regulating a quantity of the operating liquid which is discharged from the intensifying chamber into the reservoir through the discharge passage, the master cylinder piston and the input shaft being in a slidable engagement while maintaining a liquid tightness therebetween, a valve chamber being defined between the master cylinder piston and the input shaft, the discharge passage passing extending through the valve chamber, the control valve being disposed in the valve chamber to open or close the discharge passage.
With the described arrangement, the housing contains the intensifying chamber and the control valve which controls the liquid pressure introduced into the chamber, thus providing a simple and inexpensive construction with a reduced number of parts and allowing a reduction in size and allowing an increased braking force to be obtained by intensifying the master cylinder pressure.
Above and other objects, features and advantages of the invention will become apparent from the following description of the embodiments thereof with reference to the attached drawings.